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Total resistance of resistors in series

Aviation Mechanic General (AMG) practice question 10 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K11c · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONThree resistors of 1 kilohm, 3 kilohms, and 5 kilohms are connected in series. What is the total resistance of the circuit?

  1. A15 kilohms
  2. B9 kilohms
  3. C0.65 kilohm, less than the smallest resistor
Show the answer and explanation

Correct answer: B. 9 kilohms

  • A — incorrect 15 is the product of the three values, not their sum; series resistances are added.
  • B — correct For resistors in series the total resistance is the sum of the individual resistors: 1 + 3 + 5 = 9 kilohms.
  • C — incorrect A total less than the smallest resistor occurs only in a parallel circuit; in series the total is always larger than any single resistor.

BACKGROUND

In a series circuit the current must pass through each resistor one at a time, so the opposition adds up. The formula for total series resistance is RT = R1 + R2 + R3 and so on to RN. The handbook's worked voltage-drop example uses 1 kilohm, 3 kilohms, and 5 kilohms in series with a current of 1 mA, giving a total of 9 kilohms and a source voltage of 9 volts. The individual voltage drops across the resistors (1 V, 3 V, and 5 V) add up to the source voltage, which is a statement of Kirchhoff's Voltage Law.

STUDY TIP

For series circuits simply add resistances; save the reciprocal formula for parallel branches.

KEY POINTS

  • Series resistances add: RT = R1 + R2 + R3.
  • 1 k + 3 k + 5 k = 9 kilohms.
  • The total series resistance is always greater than any single resistor.

SOURCES

  • FAA-H-8083-30B ch12 "Series DC Circuits" and "Voltage Drops & Further Application of Ohm's Law" (1 k / 3 k / 5 k voltage-drop example)
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.